Devices and methods for temperature determination

ABSTRACT

A temperature determination method includes temporarily contacting a forehead of a subject with a first surface of a removable patch, and exposing a second surface of the patch opposite the first surface to ambient conditions. The method also includes sensing a temperature of the first surface of the patch while the first surface is in contact with the forehead at a first location thereon, sensing a temperature of the second surface of the patch, and calculating a sub-skull temperature of the subject based on the sensed temperatures of the first and second surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

REFERENCE TO A “SEQUENCE LISTING”

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure generally relates to devices and methods fortemperature determination and, in particular, to devices and methods forcalculating a sub-skull temperature.

2. Description of Related Art

Internal body temperature is widely used by physicians and otherhealthcare professionals as an indicator of a person's health. In mosthealthcare facilities, various non-invasive techniques may be utilizedto measure internal temperature before, during, and/or after treatment.Such techniques typically include the use of oral, rectal, tympanic, oraxial thermometers. These instruments are useful in providing asubstantially instantaneous temperature reading, but are not generallyused to provide continuous, relatively long-term monitoring of apatient's temperature. However, it is this continuous temperaturemeasurement, or the determination of relatively sudden changes inpatient temperature that is most useful to healthcare professionals whenproviding treatment. Such devices are not well-suited for continuoustemperature measurement since, for example, disposing a thermometer inthe mouth of a patient for long periods of time can cause discomfort andcan be otherwise cumbersome. Moreover, often the condition of thepatient may make it difficult or impossible to access, for example, themouth, rectum, and/or other areas of the body where temperature istypically measured with such devices.

To overcome some of these problems, devices have been developed enablingcontinuous monitoring of patient temperature. Such devices are typicallyin the form of an adhesive patch or bandage-like structure having anarray of temperature sensors. Such devices are typically adhered to thepatient's skin overlaying a portion of the temporal artery. Thesedevices, however, are characterized by deficiencies making themundesirable for use in many patient treatment settings. For example,such devices must be placed in close proximity to the temporal artery inorder to obtain an accurate temperature measurement. However, since thetemporal artery is beneath the skin, and is not easily visible, suchdevices are often mispositioned on the patient. Such mispositioning canhave adverse affects on the accuracy of the temperature measurementobtained using such devices. In addition, the temperature at the skinsurface can be significantly influenced by the ambient temperature andoften does not correlate well with core body temperature. Moreover,reducing the number of sensors employed in the sensor arrays of suchdevices reduces the accuracy of the body temperature estimation whileincreasing the number of sensors increases the cost of such devices.

The exemplary embodiments of the present disclosure overcome one or moreof the deficiencies described above.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment of the present disclosure, a temperaturedetermination method includes (a) temporarily contacting a forehead of asubject with a first surface of a removable patch, and exposing a secondsurface of the patch opposite the first surface to ambient conditions.The method also includes (b) sensing a temperature of the first surfaceof the patch while the first surface is in contact with the forehead ata first location thereon, (c) sensing a temperature of the secondsurface, and (d) calculating a sub-skull temperature of the subjectbased on the sensed temperatures of the first and second surface.

In such an exemplary embodiment, the calculated sub-skull temperature isbased on an estimated thermal resistance of the subject's skull andforehead skin, and the thermal resistance is estimated based on at leastone of an age, weight, and gender of the subject.

In other exemplary embodiments, the temperatures of the first and secondsurfaces are sensed substantially simultaneously, the calculatedsub-skull temperature is based on a known thermal resistance of thepatch, and the patch comprises a first temperature sensor associatedwith the first surface and a second temperature sensor associated withthe second surface.

In additional exemplary embodiments, the method also includescalculating a plurality of sequential sub-skull temperatures byrepeating steps (b) through (d), at a desired interval, for apredetermined period of time. In such an exemplary embodiment, themethod also includes comparing the plurality of sub-skull temperaturesto a predetermined threshold temperature and triggering an alarm inresponse to the comparison. The method also includes calculating asub-skull temperature change rate, comparing the sub-skull temperaturechange rate to a predetermined threshold change rate, and triggering analarm in response to the comparison.

In a further exemplary embodiment, the method further includes sensing ablood flow metric, the metric indicative of blood flow at the foreheadskin proximate the first surface, and comparing the sensed metric to apredetermined metric threshold. In such an exemplary embodiment, themethod includes repositioning the patch to a second location on theforehead of the subject in response to the comparison. The metric may bea change in infrared light transmissivity through the skin of theforehead. In another exemplary embodiment, sensing the metric includespassing radiation of a known wavelength through the subject's foreheadskin, and detecting the radiation proximate the first surface. In suchan exemplary embodiment, the metric may be a difference in temperaturesensed across the first surface.

The still another exemplary embodiment of the present disclosure, themethod includes maintaining the patch at the first location in responseto the comparison of the metric and the metric threshold. Such a methodalso includes calculating the sub-skull temperature using a correctionfactor corresponding to the metric, wherein the correction factor isindicative of heat flow through the forehead skin. In such a method, themetric may be arterial pulse intensity and the correction factor isgenerated based on the metric. In such a method, the metric may also bea temperature difference sensed across the first surface of the patchand the correction factor is generated based on the metric.

In an additional exemplary embodiment, sensing the metric includessubstantially simultaneously sensing temperature at a plurality oflocations along the first surface, and calculating the sub-skulltemperature includes determining a maximum difference between thetemperatures sensed at the plurality of locations.

In a further exemplary embodiment of the present disclosure, a method oftemperature determination includes removably attaching a first surfaceof a patch to a forehead of a subject, and exposing a second surface ofthe patch opposite the first surface to ambient conditions,substantially simultaneously sensing a temperature of the first andsecond surfaces while the first surface is attached to the forehead, andcalculating a sub-skull temperature of the subject based on the sensedtemperatures and an estimated thermal resistance of the subject's skulland forehead skin.

In such an exemplary embodiment, the calculated sub-skull temperature isbased on a known thermal resistance of the patch, and the method furtherincludes sensing a metric indicative of blood flow at the forehead skinproximate the first surface, and calculating the sub-skull temperaturebased on the metric.

In such an exemplary embodiment, the metric is a change in infraredlight transmissivity through the skin of the forehead, and sensing themetric includes passing radiation of a known wavelength through thesubject's forehead skin and detecting the radiation proximate the firstsurface. In additional exemplary embodiments, the metric includes atemperature gradient sensed across the first surface.

In another exemplary embodiment of the present disclosure, a temperaturedetermination device includes a patch defining a first surface and asecond surface opposite the first surface, the first surface isremovably attachable to a forehead of a subject. The device furtherincludes a first sensor positioned to detect a temperature of the firstsurface while the patch is attached to the forehead, and a second sensorpositioned to detect a temperature of the second surface while the patchis attached to the forehead.

In such an exemplary embodiment, the device further includes acontroller operably connected to the first and second sensors andconfigured to calculate a sub-skull temperature based on the detectedtemperatures of the first and second surfaces, an estimated thermalresistance of the subject's skull and forehead skin, and a known thermalresistance of the patch.

In an additional exemplary embodiment, the device includes an infraredradiation source and a third sensor configured to detect radiationemitted by the source and passing through the subject's forehead skin.

In yet another exemplary embodiment of the present disclosure, atemperature determination method includes removably attaching a firstsurface of a patch to a forehead of a subject, and exposing second andthird surfaces of the patch opposite the first surface to ambientconditions. In such a method, the second surface is separated from thefirst surface by a first patch thickness, and the third surface isseparated from the first surface by a second patch thickness differentthan the first thickness. The method also includes sensing a temperatureof the second and third surfaces while the first surface is attached tothe forehead, and calculating a sub-skull temperature of the subjectbased on the sensed temperatures of the second and third surfaces, andan estimated thermal resistance of the subject's skull and foreheadskin.

In such an exemplary embodiment, the first thickness is characterized bya first thermal resistance, and the second thickness is characterized bya second thermal resistance different than the first resistance, and themethod also includes calculating the sub-skull temperature based on thefirst and second thermal resistances. Such an exemplary method alsoincludes sensing the temperature of the second and third surfaces with anon-contact infrared sensing device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 illustrates a patch positioned on a forehead of a subjectaccording to an exemplary embodiment of the present disclosure.

FIG. 2 illustrates a patch according to an exemplary embodiment of thepresent disclosure.

FIG. 3 illustrates a partial cross-section of a forehead of the subjectwith a patch connected thereto, according to an exemplary embodiment ofthe present disclosure.

FIG. 4 illustrates a partial cross-section of a forehead of the subjectwith a patch connected thereto, according to another exemplaryembodiment of the present disclosure.

FIG. 5 illustrates a partial cross-section of a forehead of the subjectwith a patch connected thereto, according to still another exemplaryembodiment of the present disclosure.

FIG. 6 illustrates a first surface of the patch according to anexemplary embodiment of the present disclosure.

FIG. 7 illustrates a partial cross-section of a forehead of the subjectwith a patch connected thereto, according to another exemplaryembodiment of the present disclosure.

FIG. 8 illustrates a partial cross-section of a forehead of the subjectwith a patch connected thereto, according to still another exemplaryembodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-8 illustrate exemplary temperature measurement devices and/orpatches 10 useful in determining the temperature of a subject 14. Suchsubjects 14 may be, for example, human beings in need of medicaltreatment or diagnosis. As shown in FIG. 1, a patch 10 of the presentdisclosure may be connected, affixed, disposed, adhered, and/orotherwise connected to a forehead 12 of the subject 14. For example, thepatch 10 may be temporarily connected to and/or may temporarily contactat least a portion of the forehead 12 during use. Positioning the patch10 on the forehead 12 of the subject 14 may be advantageous whendetermining a temperature of the subject 14 since the forehead 12 isrelatively isolated from veins, arteries, and/or other blood flowpassages. The flow of blood through such anatomical structures may causeerror in temperature measurements and may make it more difficult tocalculate, for example, a sub-skull temperature of the subject 14. Thesub-skull temperature of the subject 14 may be, for example, a coretemperature and/or any other like internal body temperature of thesubject 14. For example, the sub-skull temperature may comprise theinternal temperature of the subject 14 distal to the frontal portion ofthe skull. As referred to herein, the forehead 12 may comprise thefrontal skull bone 32 and the layer of skin 34 positioned proximaland/or overlaying the skull bone 32 (FIG. 3).

As shown in FIG. 2, an exemplary embodiment of the patch 10 may includeone or more components configured to assist in calculating a sub-skulltemperature based on a measurement of heat flow. For example, the patch10 may include one or more operator interfaces 20. Such operatorinterfaces 20 may include one or more buttons, switches, keypads, dials,knobs, and/or other like devices configured to assist in controlling oneor more functions of the patch 10. Such operator interfaces 20 may beuseful in, for example, energizing and/or deenergizing one or morecomponents of the patch 10, toggling through and/or selecting one ormore modes of operation or display, enabling and/or disabling one ormore alarms or signals associated with patch operation, initiating asingle instantaneous sub-skull temperature calculation, initiating asubstantially continuous and/or repeating sub-skull temperaturecalculation, and/or other like modes, functions, or operations.

In an exemplary embodiment, the patch 10 may include one or morecontrollers (not shown), and each of the operator interfaces 20 may befunctionally, operably, electrically, and/or otherwise connected to thecontroller. At least one of the additional components of the patch 10may also be similarly connected to the controller, and the controllermay be configured to control the operation of each such component. In anexemplary embodiment, the controller may be configured to receivesignals, information, measurements, and/or other data from one or moresensors of the patch 10, and to calculate a sub-skull temperature of thesubject 14 based on the information received. The controller may also beconfigured to execute one or more commands and/or control programs. Forexample, the controller may be programmed to initiate one or more alarmsin response to calculating a sub-skull temperature that is greater thanor equal to a predetermined threshold temperature. In addition, thecontroller may be configured to initiate such an alarm during asubstantially continuous sub-skull temperature calculation operation ifthe calculated sub-skull temperature increases and/or decreases at arate that is greater than or equal to a predetermined thresholdtemperature change rate. In such an embodiment, the controller maysubstantially continuously calculate a sub-skull temperature changerate, and the threshold temperature and/or threshold temperature changerate may be indicative of the onset of infection and/or of a decline inthe health of the subject 14. In an exemplary embodiment, such athreshold temperature may be approximately 100° F. and such a thresholdchange rate may be approximately 0.5° F./minute. The controller may alsoinitiate such an alarm to indicate that a location of the patch 10should be changed, and such a location change alarm may be initiated inresponse to one or more sensed metrics indicative of blood flow at theforehead skin 34.

In an exemplary embodiment, the patch 10 may also include one or moredisplays 22. The display 22 may be, for example, a liquid crystal diode(LCD) screen, a light emitting diode (LED) display, a digital read-out,and/or any other like display device. The display 22 may be configuredto, for example, indicate the calculated sub-skull temperature of thesubject 14 during operation of the patch 10. The display 22 may beconfigured to display the calculated sub-skull temperature substantiallyinstantaneously and/or substantially continuously depending on the modeof operation of the patch 10. The display 22 may also be configured toindicate the mode of operation of the patch 10 (for example, continuousor instantaneous modes of sub-skull temperature calculation), as well aswhether one or more threshold temperatures, threshold temperature changerates, and/or sensed blood flow metric thresholds have been met orexceeded. As shown in FIGS. 1 and 2, the display 22 may be, for example,a substantially numerical digital display, and may also be configured todisplay any other typical operating information such as, for example atemperature vs. time trend line or other graphical depiction.

The patch 10 may also include one or more signal devices 28. Such signaldevices 28 may include, for example, one or more lights, LEDs, speakers,sirens, and/or other like devices configured to emit an audible and/oroptical alarm or signal in response to a command or signal from thecontroller. As described above, such an alarm or other signal may beinitiated by, for example, the controller when the calculated sub-skulltemperature meets or exceeds a threshold sub-skull temperature and/orwhen the sensed metric indicative of blood flow meets or exceeds ametric threshold. In additional exemplary embodiments, such an alarm orsignal may be initiated during a substantially continuous sub-skulltemperature calculation operation where the rate of sub-skulltemperature change meets or exceeds the predetermined sub-skulltemperature change rate threshold.

The patch 10 may further include one or more transponders 30. Such atransponder 30 may comprise, for example, one or more componentsconfigured to receive signals or information from a remote source, suchas a remote controller or the like. Such transponders 30 may alsoinclude one or more devices configured to transmit signals, data, and/orother information to remote receivers. For example, an exemplarytransponder 30 may be configured to transmit information correspondingto one or more sensed temperatures to a remote computer, controller, orother like device utilized in the calculation of sub-skull temperaturesof the subject 14. Such exemplary transponders 30 may facilitatecommunication with remote devices using, for example, radio, infrared,wireless, Wi-Fi, Bluetooth, and/or other like technologies. Accordingly,such a transponder 30 may enable monitoring of subjects 14 fitted withthe patch 10 from one or more remote locations within, for example, ahospital or other healthcare facility. In addition, such a transponder30 may facilitate a wireless internet connection with one or morerouters, servers, or the like.

In such an exemplary embodiment, the transponder 30 may enable ahealthcare professional to monitor one or more conditions of the subject14 remotely via a data and/or internet connection or the like. Althoughnot shown in FIG. 2, it is understood that such a patch 10 may alsoinclude one or more USB ports, communication terminals, or other likecomponents configured to facilitate connecting the patch 10 to one ormore computers, controllers, monitors, servers, routers, or other likemonitoring devices via one or more cables, wires, leads, or other likeconnection devices.

As previously discussed, the patch 10 may define at least two surfacesand, in an exemplary embodiment, the patch 10 may define a first surface16 configured to at least temporarily contact and/or be removablyattachable to the forehead 12 of the subject 14. The patch 10 may alsoinclude a second surface 18 disposed opposite the first surface 16 andconfigured to be exposed to ambient conditions such as, for example, toambient air or other like environments in a hospital and/or otherhealthcare facility. As shown in at least FIG. 3, a first sensor 24 maybe disposed at the first surface 16. In an exemplary embodiment, thesensor 24 may be embedded within the patch 10 so as to be integral withthe patch 10. Alternatively, the sensor 24 may be substantially internalto the patch 10 such that the sensor 24 may be positioned and/orotherwise configured to sense a characteristic of the first surface 16.For example, the sensor 24 may be positioned and/or otherwise configuredto sense a temperature of the first surface 16 of the patch 10 while thefirst surface 16 is in contact with and/or attached to the forehead 12.Such a sensor 24 may comprise, for example, a thermocouple, athermistor, a thermometer, a resistance temperature detector (RTD),and/or any other like device useful in measuring temperature. Inadditional exemplary embodiments, such a sensor 24 may comprise anytemperature sensitive material or coating known in the art.

In an exemplary embodiment, the sensor 24 may be substantially exposedto and/or disposed in contact with the skin 34 of the forehead 12 whilethe first surface 16 of the patch 10 is in contact with the forehead 12.Alternatively, the first surface 16 may include a relatively thin layer,wall, film, and/or other like barrier (not shown) extending between theskin 34 and the sensor 24 while the first surface 16 is in contact withthe forehead 12. Such a barrier may form at least a portion of the firstsurface 16. In such an exemplary embodiment, the thermal resistance ofsuch a barrier may be substantially negligible so as to maximize theaccuracy of the one or more measurements made by the sensor 24.Alternatively, the thermal resistance of the barrier may be known orempirically determined, and this thermal resistance may be taken intoaccount when calculating the sub-skull temperature of the subject 14. Inadditional exemplary embodiments, the sensor 24 may be configured tosense, measure, and/or otherwise detect one or more additionalproperties, conditions, and/or characteristics of the subject 14. Forexample, in addition to temperature, the sensor 24 may be configured todetect heart rate, blood pressure, electrical current, and the like.

The sensor 26 may be substantially identical to the sensor 24. As shownin, for example, FIGS. 2 and 3, the sensor 26 may be disposed at and/orproximate to the second surface 18. In an exemplary embodiment, thesensor 26 may be exposed to ambient conditions, while in additionalexemplary embodiments, the second surface 18 may include a layer, wall,film, and/or barrier (not shown) similar to that described above withregard to the first surface 16. In such an exemplary embodiment, thebarrier may extend between the sensor 26 and the ambient environment toprotect the sensor 26 from contaminants, wet conditions, and/or otherpotentially damaging or harmful environmental elements. Similar to thebarrier discussed above with regard to the first surface 16, a likebarrier may form at least a portion of the second surface 18 and mayhave a substantially negligible thermal resistance so as not to hinderthe accuracy of measurements obtained by the sensor 26. Alternatively,the thermal resistance of such a barrier may be taken into account whencalculating the sub-skull temperature. Although shown in FIG. 3 asincluding two sensors 24, 26, in additional exemplary embodiments, thepatch 10 may include any number of additional sensors configured toassist in sensing conditions of the subject 14 and/or the patch 10 suchas temperature, blood pressure, heart rate, and/or other like metrics.Such additional sensors may be disposed at or along any of the surfaces16, 18 of the patch 10 and/or at any other useful position along and/orwithin the patch 10.

The patch 10 may be made from any substantially rigid medically approvedmaterial known in the art. Such materials may include, for example,plastics, rubber, polymers, synthetic materials, cloth, mesh, and/orcombinations thereof. For example, the patch 10 may be made frommaterials similar to removable bandages or other like materials. Thesematerials may allow for breathability during use and for easy disposalonce use is complete. In addition, such patch materials may besubstantially flexible, substantially light-weight, and/or relativelycomfortable such that a patch 10 may be disposed on and/or removablyattached to the forehead 12 of a subject 14 for extended periods oftime. To assist with such removable connection, any known adhesive maybe disposed on at least a portion of the first surface 16.Alternatively, one or more elastic straps, headbands, belts, ties, orthe like may be connected to at least a portion of the patch 10 toassist in removably attaching the patch 10 to the forehead 12.

The patch 10 may have a known thermal resistance, and such thermalresistance may depend upon, for example, the thickness A of the patch 10as well as the one or more materials utilized to form the patch 10. Thethermal resistance of the plastics, rubber, polymers, or other materialsused to form the patch 10 may be known in the art, and the sub-skulltemperature calculated in accordance with one or more of the exemplarymethods described herein may be based upon the known thermal resistanceof the patch 10.

As will be described in greater detail with regard to FIGS. 7 and 8, inexemplary embodiments of the present disclosure, the patch 10 may haveone or more thicknesses. For example, a first portion 60 of the patch 10may have a first thickness D between the first surface 16 and a secondsurface 48. A second portion 62 of such an exemplary patch 10 may alsohave a second thickness E between the first surface 16 and a thirdsurface 50. Moreover, exemplary patches 10 of the present disclosure maybe made from more than one material, and each portion of the patch 10may have a unique thermal resistance depending upon the materialsutilized to form the particular portion of the patch and/or the relativethickness of the portion. For example, the first portion 60 of the patch10 shown in FIGS. 7 and 8 may be made from a first material and thesecond portion 62 of the patch 10 may be made from a second materialdifferent than the first material. In such an exemplary embodiment, thedifferent portions 60, 62 of the patch 10 may have unique differentthermal resistances. The different thermal resistances of each portion60, 62 of the patch 10 may be taken into account when calculating, forexample, the sub-skull temperature of the subject 14.

In an exemplary embodiment, a sub-skull temperature may be calculated bysensing one or more temperatures associated with the forehead skin 34and/or patch 10 while the patch 10 is at least temporarily contactingand/or removably attached to the forehead 12. For example, in order tocalculate a sub-skull temperature, a temperature of a surface of thepatch 10 contacting the forehead 12 may be sensed along with atemperature of another surface of the patch 10 disposed away from theforehead 12. In additional exemplary embodiments, such temperaturemeasurements may be taken at two different predetermined levels ordepths within the various thicknesses of the patch 10, and along theheat transfer flow path. In such embodiments, the sensors 24, 26 may bepositioned at such predetermined depths within the patch 10 fortemperature measurement. According to basic heat transfer theory, thequantitative value of heat flow (q) is generally equal to the amount ofheat energy passing through a given system over time. Such heat flow isgoverned by the resistance of the system as well as the temperature dropacross the system. In the case of a subject 14, the core and/orsub-skull temperature of the subject 14 can be solved for utilizingthese heat flow relationships.

In calculating the sub-skull temperature (T_(sub-skull)) of a subject14, the temperature of the outer surface of the forehead skin 34 can bemeasured and/or otherwise sensed using a patch 10 disposed thereon.Alternatively, once the patch 10 has been disposed in contact with theforehead 12, the first surface 16 of the patch 10 may achievesubstantially the same temperature as the outer surface of the foreheadskin 34. Thus, in an alternative exemplary embodiment, the temperatureof the first surface 16 of the patch 10 (T₁) may be sensed and, thissurface temperature (T₁) may be utilized in the sub-skull temperaturecalculation.

In addition, a temperature of the second surface 18 of the patch 10 (T₂)disposed opposite the first surface 16 and away from the forehead 12 mayalso be sensed. As described above, the second surface 18 may beseparated from the first surface 16 by the thickness A of the patch 10.The temperatures T₁, T₂ of the first and second surfaces 16, 18 may beused to calculate the amount of heat flowing out of the forehead 12, andthus the sub-skull temperature T_(sub-skull) of the subject 14,according to the following equation:

T _(sub-skull) =T ₁ +R(T ₁ −T ₂).  [1]

In the above equation, “R” may be a constant that is estimated and/orempirically determined based upon the physical characteristics of thesubject 14 and/or the patch 10. In particular, the constant R may be athermal resistance associated with the skull 32 and/or skin 34 of theforehead 12. In an exemplary embodiment, the constant R may representthe thermal resistance of the forehead 12 consisting of both the skull32 and skin 34. The value of the constant R utilized in the sub-skulltemperature calculation may vary within a relatively limited range basedon one or more physical characteristics of the subject 14. For example,a range of constants R may be estimated and/or empirically determinedbased upon at least one of the age, weight, gender, and/or othercharacteristics of the subject 14, and the values of such constants Rmay have a variation on the order of, approximately, 20%. In calculatingthe sub-skull temperature of a particular subject 14, a constant R maybe chosen based upon whether the subject 14 is a small child, anaverage-sized adult, a large adult, and/or an elderly adult. Inaddition, the chosen constant R may vary for males as opposed tofemales, in any of the above age ranges or categories.

The value of each constant R may also be based upon the thermalresistance of the patch 10. The thermal resistance of the patch 10 maybe dependent upon the physical construction and/or thermalcharacteristics of the patch 10 such as, for example, the materials usedto form the patch 10 and/or the one or more thicknesses thereof. In anexemplary embodiment, the constant R may be calculated by dividing thethermal resistance of the forehead 12 by the thermal resistance of thepatch 10. In exemplary embodiments, the constant R may be determinedthrough experimentation and/or through one or more clinical trialsutilizing different constructions and/or embodiments of the patch 10 tomeasure and/or calculate sub-skull temperature of subjects 14 having avariety of different ages, weights, genders, and/or other physicalcharacteristics. A healthcare professional may then determine whichconstant R to use for a given subject 14 and patch 10 using one or morelook-up tables or other like listings.

In additional exemplary embodiments, the calculated sub-skulltemperature of the subject 14 may be based on one or more physicalcharacteristics, conditions, and/or other metrics associated with thesubject 14 and indicative of blood flow. For example, in calculatingsuch a sub-skull temperature, a healthcare professional may measure,determine, and/or otherwise sense a metric indicative of blood flow atthe forehead skin 34 of the subject 14. Significant blood flow proximatethe first surface 16 of the patch 10 may cause error in temperatureand/or other measurements obtained with the patch 10. For these reasons,it may be desirable and/or advantageous to avoid positioning the patch10 proximate the temporal artery, or other veins or arteries of thesubject 14. The forehead 12 of the subject 14 may be particularly wellsuited for calculating sub-skull temperature according to the exemplarymethods described herein because the forehead 12 is generally free fromsuch blood flow passageways. Accordingly, sensing a metric indicative ofblood flow at the forehead skin 34 may assist in minimizing and/orsubstantially illuminating error in the sub-skull temperaturecalculation.

In exemplary embodiments in which the sensor 24 is disposed at and/orotherwise configured to sense a temperature of the first surface 16, itmay be advantageous to sense the metric indicative of blood flow at anarea of the forehead 12 proximate the first surface 16 of the patch 10.If the metric indicates an insignificant level of blood flow through theskin 34 that is proximate the first surface 16, the blood flow can beignored in the calculation of sub-skull temperature. However, if thepatch 10 is disposed at an area of the forehead 12 where significantblood flow is detected, the patch 10 may be repositioned on the forehead12 to an area characterized by lower and/or insignificant blood flowlevels. In further exemplary embodiments in which the metric indicatesblood flow that is below a maximum threshold level requiringrepositioning of the patch but that is above a minimum significancethreshold, the metric may be taken into account when calculating thesub-skull temperature and the patch 10 may not be repositioned. Instead,as will be described below, the sensed metric may be used to generate acorrection factor that can be incorporated into the sub-skulltemperature calculation.

In an exemplary embodiment, a periodic or pulsating change in thetransmissivity of radiation passing through at least a portion of theforehead 12 may be used as a metric indicative of blood flow. Forexample, one or more beams of radiation may be passed through at least aportion of the forehead 12, and as such radiation passes through theforehead 12, the radiation may be slowed, deflected, defracted,reflected, and/or otherwise acted upon by components of the foreheadand/or body functions or conditions of the subject 14. Such bodyfunctions may include, for example, arterial blood flow. As shown inFIG. 4, one or more beams of radiation 40 having a known wavelength maybe passed through the skin 34 of the forehead 12 during an exemplarysub-skull temperature determination method. Such radiation 40 may thenbe detected and/or otherwise sensed as it passes along, beneath, and/orproximate to the first surface 16 of the patch 10. One or morecharacteristics of the radiation 40 may be altered as it passes throughthe skin 34, and the pulsating changes in such characteristics may beindicative of arterial blood flow through the skin 34 of the forehead12. For example, significant levels of blood flow through the skin 34may cause a corresponding relative change in the wavelength, frequency,amplitude, direction, and/or other characteristics of such radiation 40as the radiation passes through the skin 34. Accordingly, detecting suchradiation 40 passing through the skin 34 and/or determining the changein such radiation characteristics may be useful in determining thepresence and/or amount of blood flow proximate the patch 10.

To facilitate the sensing of such a metric, an exemplary embodiment ofthe patch 10 may include, for example, at least one radiation source 36.The radiation source 36 may be, for example, an LED, a low power laser,an incandescent light bulb, and/or any other known light sourceconfigured to controllably emit radiation of a known wavelength,frequency, amplitude, and/or other controllable characteristic. In anexemplary embodiment, any known LED configured to emit radiation in theinfrared spectrum, such as the Siemens SFH487 LED, may be employed. Inother exemplary embodiments, the radiation source 36 may comprise, forexample, a quantum cascade laser, or other known light source configuredto emit radiation in the thermal band. Such radiation sources 36 may beshaped, sized, powered, and/or otherwise configured for safe usageproximate the skin 34 of the subject 14. For example, such radiationsources 36 may be configured for substantially direct contact with theskin 34 during use, and may be capable of substantially constantoperation over relatively long periods of time without harming the skin34 or causing discomfort to the subject 14.

In another exemplary embodiment, the sensed metric indicative of bloodflow may be oxygen saturation. For example, the ratio of oxyhemoglobinto the total concentration of hemoglobin present in the blood may besensed and/or otherwise measured at the skin 34 of the forehead 12, anda sub-skull temperature may be calculated based on such a metric. Insuch an exemplary embodiment, arterial oxyhemoglobin saturation may bemeasured using any of a number of non-invasive pulse oximetry devicesusing a reflective SpO₂ methodology. In such exemplary embodiments, theradiation source 36 may comprise or may be a component of any of anumber of known oxygen saturation level measurement devices. Suchdevices may include a pulse oximeter or CO-oximeter, and in an exemplaryembodiment, any known SpO₂ device such as the Nellcor™ Oximax™ Max-Fast™forehead sensor may be employed. Such devices may be useful in providingnon-invasive measurement of arterial blood oxygen saturation as well aspulse rate. Such devices may employ two or more radiation sources 36 togenerate beams of infrared and/or other radiation 40 passing through theskin 34, venous vessels, bone, skull 32, and/or other body parts.Because variable amounts of such radiation 40 is absorbed and reflectedas blood volume increases and decreases (during systole and diastole)the ratio of light absorption at systole and diastole may be translatedinto a measurement of oxygen saturation. Such a metric may then beutilized by methods of the present disclosure to indicate that the patch10 should be repositioned and/or to assist in calculating the sub-skulltemperature of the subject 14 due to indications of significant bloodflow proximate the patch 10 in its current position.

In such exemplary embodiments, the patch 10 may also include one or morereceivers 38 and/or other additional components of such oxygensaturation measurement devices. As shown in FIG. 4, such receivers 38and/or other additional components may be disposed proximate the firstsurface 16 and/or may be otherwise embedded within the patch 10 tofacilitate measurements proximate the first surface 16 and/or at theskin 34. In an exemplary embodiment, the receiver 38 may comprise one ormore sensors, photo transistors, or other like detection devicesconfigured to sense, detect, and/or otherwise measure the wavelength,frequency, amplitude, reflection, refraction, absorption, and/or otherquantifiable characteristic of the radiation 40 emitted by the source36. Any known sensor configured to measure the intensity of thereflected radiation 40, such as the Siemens SFH 309FA may be employed.For example, the receiver 38 and/or other components may be configuredto instantaneously, periodically, and/or substantially continuously scanfor blood flow and/or blood flow pulsations in the skin 34 proximate thefirst surface 16 of the patch 10.

In an exemplary sub-skull temperature calculation method, the patchshown in FIG. 4 may be removably attached to the forehead 12 of thesubject 14, and the source 36 and receiver 40 may perform one or morereflective SpO₂ measurements of the type described above. If no arterialpulsations are detected, or if the sensed pulsations are indicative ofblood flow below a minimum blood flow threshold, the patch 10 may beindicated to be disposed in an area where blood flow through the skin 34will have substantially no impact on the calculated sub-skulltemperature. Accordingly, equation [1] above can be used to accuratelydetermine T_(sub-skull) without repositioning the patch 10. In anexemplary embodiment, such a minimum threshold may correspond to SpO₂pulsation intensity measurements equal to approximately 0.5%.

In such an exemplary embodiment, if the sensed pulsations are indicativeof blood flow that is above a maximum threshold level, the controllermay operate the display 22 and/or the signal device 28 to indicate thatthe patch 10 must be repositioned to an area of the forehead 12characterized by less blood flow. In an exemplary embodiment, such amaximum threshold may correspond to SpO₂ pulsation intensitymeasurements equal to approximately 2.0%.

Moreover, in such an exemplary embodiment, if the sensed pulsations areindicative of blood flow that is greater than or equal to the minimumthreshold discussed above and less than or equal to the maximumthreshold, the intensity and/or other characteristics of the sensedpulsations may be used to add a correction factor to the sub-skulltemperature calculation. Such a correction factor (CF_(p)) maycompensate for heat flow (stray conduction) caused by blood movingthrough the skin 34 proximate the first surface 16. The amount of suchstray conduction is a function of blood flow and near-surface bloodtemperature, and the correction factor CF_(p) may be calculatedaccording to the following equation:

CF _(p) =SC _(p)(pulsation strength)(T ₁ −T ₂).  [2]

In the above equation, “SC_(p)” may be an empirically derived constantconverting the pulsatile blood flow measurement to a temperatureadjustment due to stray conduction effects. In addition, “pulsationstrength” may be a percentage or other arterial blood flow value sensedand/or output during the above SpO₂ measurements. Thus, in such anexemplary embodiment, equation [1] above can be modified to calculatesub-skull temperature as follows:

T _(sub-skull) =T ₁ +R(T ₁ −T ₂)+CF _(p).  [3]

In still another exemplary embodiment of the present disclosure, ametric indicative of blood flow at and/or otherwise through the foreheadskin 34 may include one or more temperature gradients caused by and/orresulting from substantially lateral blood flow through the skin 34.Because blood flow through the forehead skin 34 is typicallydirectional, a temperature gradient may be observed, measured, and/orotherwise sensed at the skin 34 proximate the first surface 16 of thepatch 10. In an exemplary embodiment, such a temperature gradient may besensed across the first surface 16 even after the patch 10 has beenattached and/or disposed in contact with the skin 34 for a timesufficient for the patch 10 to reach a level of substantial thermalstability.

In such an exemplary embodiment, relatively minimal blood flow mayresult in a corresponding temperature gradient of minimal magnitude.However, more substantial blood flow through the skin 34 at the forehead12 may result in a temperature gradient that is correspondingly largerin magnitude. As described above with, for example, the embodiment ofFIG. 4, a temperature gradient sensed across the first surface 16 of thepatch 10 may be taken into account in determining whether the patch 10should be repositioned on the forehead 10 and/or when calculating asub-skull temperature of the subject 14. Accounting for the presenceand/or strength of such a temperature gradient may increase the accuracyof sub-skull temperature calculations.

In an exemplary embodiment, one or more temperatures may besubstantially continuously sensed at a plurality of locations along thefirst surface 16. In such an exemplary embodiment, a temperaturegradient and/or difference sensed between any two points along the firstsurface 16 may be indicative of the existence of blood flow and/or theamount or volume of blood flow proximate the first surface 16. Sensingsuch temperatures at a plurality of locations along the first surface 16may also be useful in evaluating the direction of blood flow through theskin 34.

As shown in FIGS. 5 and 6, the patch 10 may include more than one sensordisposed at and/or proximate to the first surface 16. For example, thepatch 10 may include a plurality of sensors 42, 44, 46 disposed at adifferent location along the first surface 16. In an exemplaryembodiment, such sensors 42, 44, 46 may be disposed proximate aperiphery of the first surface 16 and/or may be optimally spaced alongthe first surface 16 to maximize the area of the skin 34 capable ofbeing sensed. Such spacing may also maximize the ability of the sensors42, 44, 46 to evaluate blood flow in multiple different directionsthrough the skin 34. The sensors 42, 44, 46 may comprise, for example,any known thermocouple, thermistor, thermometer, RTD, temperaturesensitive material, temperature sensitive coating, and/or light sensingdevice, and in an exemplary embodiment, the sensors 42, 44, 46 may besubstantially similar to the sensors 24, 26 described above. In anexemplary embodiment in which the patch 10 includes more than one sensor42, 44, 46 disposed at and/or proximate to the first surface 16, thesensor 24 described above may be one of the sensors 42, 44, 46. Suchsensors 42, 44, 46 may also be electrically, controllably, and/orotherwise operably connected to the controller (not shown) of the patch10 described herein. Although shown in a substantially triangulararrangement in FIG. 6, it is understood that the sensors 42, 44, 46 maybe arranged in any pattern and/or other configuration along the firstsurface 16. For example, in additional exemplary embodiments, the patch10 may include any number of additional sensors along the first surface16, and such sensors may be arranged in a circular pattern.Alternatively, the patch 10 may include at least one sensor disposed ateach corner of the first surface 16 to assist in observing and/orotherwise sensing a temperature gradient along the first surface 16.

In an exemplary sub-skull temperature calculation method, the patch 10shown in FIGS. 5 and 6 may be removably attached to the forehead 12 ofthe subject 14, and the multiple sensors 42, 44, 46 disposed at thefirst surface 16 of the patch 10 may instantaneously and/orsubstantially continuously sense the temperature of the first surface 16at the various respective sensor locations. Information corresponding tothese sensed temperatures may then be sent to the controller. Ifsubstantially no measurable difference in temperature is sensed amongthe various sensors 42, 44, 46, or if the greatest difference betweenthe various sensed temperatures is below a minimum temperaturedifference threshold, the patch 10 may be disposed in an area of theforehead 12 where blood flow through the skin 34 may have substantiallyno impact on the calculated sub-skull temperature. Accordingly, equation[1] above may be used to accurately determine the sub-skull temperaturewithout repositioning the patch 10 on the forehead 12. In an exemplaryembodiment, such a minimum threshold may be, approximately 0.5° F.

In such an exemplary embodiment, if the difference between the lowestsensed temperature and the highest sensed temperature is above a maximumtemperature difference threshold, such a detected temperature gradientmay be indicative of blood flow levels that may cause an unacceptablelevel of error in the sub-skull temperature calculation. If such adifference exists, the controller may operate the display 22 and/or thesignal device 28 to indicate that the patch 10 must be repositioned toan area of the forehead 12 characterized by less blood flow. In anexemplary embodiment, such a maximum threshold may be approximately 1.5°F.

Moreover, in such an exemplary embodiment, if the difference between thelowest sensed temperature and the highest sensed temperature is greaterthan or equal to the minimum temperature difference threshold discussedabove and less than or equal to the maximum temperature differencethreshold, such a detected temperature difference and/or gradient may beused to add a correction factor to the sub-skull temperature calculationsimilar to the correction factor CFp discussed above with regard to theexemplary embodiment of FIG. 4. For example, the amount of heat flow(stray conduction) caused by blood moving through the skin 34 proximatethe first surface 16 can be estimated using the sensed cross-patchtemperature gradient detected by the sensors 42, 44, 46. Similar to theprocess described above with regard to FIG. 4, in the exemplaryembodiment of FIG. 6, equation [1] above can be modified to calculatesub-skull temperature as follows:

T _(sub-skull) =T ₁ +R(T ₁ −T ₂)+CF _(t).  [4]

In the above equation, the correction factor “CF_(t)” may compensate forheat flow (stray conduction) caused by blood flow moving through theskin 34, and the correction factor CF_(t) may be calculated according tothe following equation:

CF _(t) =SC _(t)(Δ_(Tmax))(T ₁ −T ₂).  [5]

In the above equation, “SC_(t)” may be an empirically derived constantconverting the cross-patch temperature gradient to a temperatureadjustment due to stray conduction effects. In addition, “Δ_(Tmax)” maybe the difference between the lowest sensed temperature and the highestsensed temperature.

In additional exemplary embodiments, a sub-skull temperature of thesubject 14 may be calculated based on sensed temperatures of two or moresurfaces of the patch 10 that are spaced from and/or otherwise not indirect physical contact with the skin 34 of the forehead 12. In such anexemplary embodiment, the first surface 16 of the patch 10 may beremovably attached to the skin 34 of the forehead 12 as described above.As shown in FIGS. 7 and 8, such an exemplary patch 10 may include two ormore portions 60, 62 having different respective thicknesses. Forexample, the first portion 60 of the patch 10 may have a thickness D,and this first portion 60 may define a second surface 48 that isseparated from the first surface 16 by the thickness D. In addition, thesecond portion 62 of such an exemplary patch 10 may define a secondpatch thickness E that is different than the first patch thickness D.The second portion 62 may define a third surface 50 that is spaced fromthe first surface 16 by the thickness E. As shown in FIGS. 7 and 8, thesecond surface 48 may be disposed substantially parallel to the thirdsurface 50, and both surfaces 48, 50 may be disposed substantiallyparallel to the first surface 16. Alternatively, in additional exemplaryembodiments, the second surface 48 may be disposed at any obtuse oracute angle relative to the third surface 50. In addition, the secondand third surfaces 48, 50 may be disposed at any desirable anglerelative to the first surface 16.

Any of the patches 10 described herein may be made from more than onematerial. Such exemplary patches 10 may define a single substantiallyuniform thickness, or alternatively, various portions of the patch 10made from different materials may have unique different thickness and/orthermal resistances. For example, the patch 10 illustrated in FIGS. 7and 8 may be made from at least one material and, in further exemplaryembodiments, the first portion 60 of the patch 10 associated with thesecond surface 48 may be made from a first material, and the secondportion 62 of the patch 10 associated with the third surface 50 may bemade from a second material different than the first material. The patch10 illustrated in FIGS. 7 and 8 may be made from one or more of thematerials described above with regard to the patches 10 of previousembodiments, and in the exemplary embodiment of FIGS. 7 and 8, the firstthickness D and/or the first portion 60 of the patch 10 defining thesecond surface 48 may be characterized by a first thermal resistance. Inaddition, the second thickness E and/or the second portion 62 of thepatch 10 defining the third surface 50 may be characterized by a secondthermal resistance that is different from the first thermal resistanceof thickness D. In additional exemplary embodiments, a patch 10 having asingle substantially uniform thickness may be made from two or moredifferent materials, each characterized by different respective thermalresistances. Thus, a patch 10 having different portions characterized bydifferent respective thermal resistances may be formed and/or achievedby material selection and/or thickness selection. In calculating asub-skull temperature utilizing a patch 10 having portions characterizedby more than one thermal resistance, such as the exemplary patch 10illustrated in FIGS. 7 and 8, the respective different thermalresistances may each be taken into account. Such a calculation may beaccomplished utilizing, for example, equations [6] or [7] below.

In addition to calculating a sub-skull temperature based on thedifferent thermal resistances of portions 60, 62, such a calculation mayalso be based on sensed temperatures of the second and third surfaces48, 50. In such an exemplary embodiment, the temperatures of the secondand third surfaces 48, 50 may be sensed while the first surface 16 isconnected and/or removably attached to the forehead 12 of the subject14. As shown in FIG. 7, an exemplary embodiment of the patch 10 mayinclude a sensor 26 disposed at and/or otherwise associated with thesecond surface 48 and another sensor 28 disposed at and/or otherwiseassociated with the third surface 50. As described above, such sensors26, 28 may be electrically, controllably, and/or otherwise operablyconnected to a controller (not shown) of the exemplary patch 10, so asto assist in sensing the temperature of the second and third surfaces48, 50 and calculating the sub-skull temperature of the subject 14. Inparticular, in the embodiment of FIG. 7, the sensor 26 may be configuredto sense a temperature of the second surface 48 (T_(second surface)),and the sensor 28 may be configured to sense the temperature of thethird surface 50 (T_(third surface)). These two patch surfacetemperatures, as well as an estimated thermal resistance R of thesubject's skull 32 and forehead skin 34 may be utilized to calculate anexemplary sub-skull temperature. Such a calculation my be accomplishedutilizing, for example, the equations:

T _(sub-skull) =T _(third surface) +R(T _(third surface) −T_(second surface)),  [6]

or

T _(sub-skull) =T _(second surface) +R(T _(third surface) −T_(second surface)).  [7]

As shown in FIG. 8, in additional exemplary embodiments, one or both ofthe sensors 26, 28 shown in FIG. 7 may be omitted. For example, therespective temperatures of the second surface 48

(T_(second surface)) and third surface 50 (T_(third surface)) may stillbe utilized to calculate the sub-skull temperature of the subject 14,however, in the embodiment of FIG. 8, the two surface temperatures maybe sensed utilizing any of a number of known non-contact thermometrymethods. For example, a non-contact sensing device 56 may be employed todetect the respective temperatures of the second and third surfaces 48,50. In such an exemplary embodiment, the sensing device 56 may includeone or more sensors 58 configured to acquire such temperatures withoutcontacting the respective surfaces 48, 50. In such an exemplaryembodiment, the device 56 may include any known infrared thermometrydevice configured to assist in obtaining such temperatures.

In such an exemplary embodiment, the patch 10 may define one or moretargets 52, 54 associated with the respective surfaces 48, 50 to assistin sensing the temperature of these surfaces. Such targets 52, 54 maycomprise, for example, one or more notches, cut-outs, divots, dimples,bubbles, ridges, flats, shoulders, and/or any other substantiallyplanar, substantially convex, and/or substantially concave structureuseful is assisting the non-contact sensing device 56 in obtaining anaccurate temperature measurement. Moreover, the one or more sensors 58associated with the non-contact sensing device 56 may be configured tosense one or more characteristics of the ambient environment in whichthe patch 10 is being used, such as ambient temperature. In such anexemplary embodiment, the sub-skull temperature of the subject 14 may becalculated utilizing the following equation:

T _(sub-skull) =T _(third surface) −T _(second surface)*(R1/R2)((T_(second surface) −T _(ambient))/(T _(third surface)−Ta)))/((1−(R1/R2)*((T _(second surface) −T _(ambient))/(T_(third surface) −T _(ambient)))).  [8]

In the above equation, it is understood that “R1” represents thecombined thermal resistance of the forehead 12 and thickness D, “R2”represents the combined thermal resistance of the forehead 12 andthickness E, and “T_(ambient)” represents the ambient temperaturemeasured by, for example, the sensor 58.

The invention has been described in detail with particular reference toa presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. The presently disclosed embodiments are, therefore,considered in all respects to be illustrative and not restrictive. Thescope of the invention is indicated by the appended claims, and allchanges that come within the meaning and range of equivalents thereofare intended to be embraced therein.

1. A temperature determination method, comprising: (a) temporarilycontacting a forehead of a subject with a first surface of a removablepatch, and exposing a second surface of the patch opposite the firstsurface to ambient conditions; (b) sensing a temperature of the firstsurface of the patch while the first surface is in contact with theforehead at a first location thereon; (c) sensing a temperature of thesecond surface of the patch; and (d) calculating a sub-skull temperatureof the subject based on the sensed temperatures of the first and secondsurface.
 2. The method of claim 1, wherein the calculated sub-skulltemperature is based on an estimated thermal resistance of the subject'sskull and forehead skin.
 3. The method of claim 2, wherein the thermalresistance is estimated based on at least one of an age, weight, andgender of the subject.
 4. The method of claim 1, wherein thetemperatures of the first and second surfaces are sensed substantiallysimultaneously.
 5. The method of claim 1, wherein the calculatedsub-skull temperature is based on a known thermal resistance of thepatch.
 6. The method of claim 1, wherein the patch comprises a firsttemperature sensor associated with the first surface and a secondtemperature sensor associated with the second surface.
 7. The method ofclaim 1, further comprising calculating a plurality of sequentialsub-skull temperatures by repeating steps (b) through (d), at a desiredinterval, for a predetermined period of time.
 8. The method of claim 7,further comprising comparing the plurality of sub-skull temperatures toa predetermined threshold temperature and triggering an alarm inresponse to the comparison.
 9. The method of claim 7, further comprisingcalculating a sub-skull temperature change rate comparing the sub-skulltemperature change rate to a predetermined threshold change rate, andtriggering an alarm in response to the comparison.
 10. The method ofclaim 1, further comprising sensing a blood flow metric, the metricindicative of blood flow at the forehead skin proximate the firstsurface, and comparing the sensed metric to a predetermined metricthreshold.
 11. The method of claim 10, further comprising repositioningthe patch to a second location on the forehead of the subject inresponse to the comparison.
 12. The method of claim 10, furthercomprising maintaining the patch at the first location in response tothe comparison.
 13. The method of claim 12, further comprisingcalculating the sub-skull temperature using a correction factorcorresponding to the metric.
 14. The method of claim 13, wherein thecorrection factor is indicative of heat flow through the forehead skin.15. The method of claim 13, wherein the metric comprises arterial pulseintensity and the correction factor is generated based on the metric.16. The method of claim 13, wherein the metric comprises a temperaturedifference sensed across the first surface of the patch and thecorrection factor is generated based on the metric.
 17. The method ofclaim 10, wherein sensing the metric comprises passing radiation of aknown wavelength through the subject's forehead skin, and detecting theradiation proximate the first surface.
 18. The method of claim 10,wherein sensing the metric comprises substantially simultaneouslysensing temperature at a plurality of locations along the first surface,and calculating the sub-skull temperature comprises determining amaximum difference between the temperatures sensed at the plurality oflocations.
 19. A temperature determination device, comprising: (a) apatch defining a first surface and a second surface opposite the firstsurface, the first surface removably attachable to a forehead of asubject; (b) a first sensor positioned to detect a temperature of thefirst surface while the patch is attached to the forehead; and (c) asecond sensor positioned to detect a temperature of the second surfacewhile the patch is attached to the forehead.
 20. The device of claim 19,further comprising a controller operably connected to the first andsecond sensors and configured to calculate a sub-skull temperature basedon the detected temperatures of the first and second surfaces, anestimated thermal resistance of the subject's skull and forehead skin,and a known thermal resistance of the patch.
 21. The device of claim 19,further comprising an infrared radiation source and a third sensorconfigured to detect radiation emitted by the source and passing throughthe subject's forehead skin.
 22. A temperature determination method,comprising: (a) removably attaching a first surface of a patch to aforehead of a subject, and exposing second and third surfaces of thepatch opposite the first surface to ambient conditions, the secondsurface being separated from the first surface by a first patchthickness, and the third surface being separated from the first surfaceby a second patch thickness different than the first thickness; (b)sensing a temperature of the second and third surfaces while the firstsurface is attached to the forehead; and (c) calculating a sub-skulltemperature of the subject based on the sensed temperatures of thesecond and third surfaces, and an estimated thermal resistance of thesubject's skull and forehead skin.
 23. The method of claim 22, whereinthe first thickness is characterized by a first thermal resistance, andthe second thickness is characterized by a second thermal resistancedifferent than the first resistance, the method further comprisingcalculating the sub-skull temperature based on the first and secondthermal resistances.
 24. The method of claim 22, further includingsensing the temperature of the second and third surfaces with anon-contact infrared sensing device.